The use of propellers providing adjustable pitch is of importance regarding many ships, to enable optimization of the propulsion. A conventional system to arrange for adjustability of the pitch of the propellers is based on a rather powerful hydraulic system. For many ships hydraulic systems requiring about 30 kW power are needed. It is evident that such a large need output of power implies disadvantages. This is especially apparent taking into account that there is always some leakage in big hydraulic systems and therefore the system has to be up and running more or less continuously, not at least to achieve sufficient cooling. As a consequence such an hydraulic system is rather costly. Moreover it leads to the creation of noise, which in many installations is undesired. Furthermore it necessitates a rather complex shaft design, since the shaft has to enable both supply and drainage from the two pressure chambers used in connection with a hydraulic piston that actuates positioning of the propeller pitch adjustment device. Finally it is also a hazardous design with regard to the environment, since it may lead to leakage of oil into the nature.
From U.S. Pat. No. 5,498,135 there is known a Propeller Pitch Control Arrangement, comprising a propeller hub having a number of interface fittings for adjustable pitch positioning of a propeller blade, a positioning device, within said hub, having a number of propeller control interfaces and an actuator arrangement, comprising a motor device (in the form of an electrical motor) positioned adjacent said hub, arranged to move and position said positioning device to enable varying pitch for said propeller blades. However, this known solution uses a reduction gear in combination with a drive spool and pitch ring, which makes the design bulky and complex, which probably is the reason why that design concept has not been any success. Also WO9631390 and US 20040157509, in a similar manner present solutions that are bulky and complex, e.g. by the use of a non-unitary hub body in WO9631390 and by the use of an adjustment device forming multiple bodies in US 20040157509.